1. Field of the Invention
This invention relates to a flat panel display that has a phase shift layer and a reflecting layer stacked on an opposite electrode to destructively interfere with reflected external light to realize black. The invention also relates to a method of fabricating the flat panel display.
2. Discussion of the Background
An organic light emitting display (OLED) has a contrast ratio depending on the intensity of external light. A black matrix material may be employed to improve the contrast ratio, but it is very difficult to realize perfect black by shielding the external light in an emission region.
One device used in the prior art to attempt to solve this problem is a circular polarizer 140 shown in FIG. 1. U.S. Pat. No. 5,596,246 discloses an OLED that employs the circular polarizer 140. The OLED includes a circular polarizer 140, a lower substrate 100, a transparent first electrode 110, an organic emission layer 120, and a reflecting second electrode 130.
The circular polarizer 140 is employed to reduce the amount of external light that is reflected off a display panel. The circular polarizer 140 includes a linear polarizer 145 and a quarter compensating plate 141. Two axes of the quarter compensating plate 141 form a 45° angle to an axis of the linear polarizer 145. External light passes through the linear polarizer 145 and becomes linearly polarized. The quarter compensating plate 141 rotates the polarized light 45° spirally. The rotation direction of the polarized light is reversed after it is reflected from a reflecting layer of the display. The polarized light is rotated another 45° when it passes back through the quarter compensating plate 141. At this point, the polarized light is perpendicular to the linear polarizer and is therefore blocked by the linear polarizer 145.
Only about 44% of light emitted from the organic emission layer 120 passes through the circular polarizer 140. A large amount of light emitted from the organic emission layer 120 is absorbed by the circular polarizer 140, which causes the luminous efficiency and the contrast ratio to be low. To compensate for the reduced luminance, a relatively high voltage must be applied to achieve the desired luminance, which increases the power consumption and decreases the life span of the display. Furthermore, the manufacturing costs of the OLED are increased because the manufacturing process is complicated and the polarizer is expensive.
Another device used in the prior art to attempt to solve this problem was developed by Luxell Technologies Inc. Instead of a polarizer, Luxell incorporated an absorbing layer and a dielectric layer between an inorganic phosphorescent layer and an opposite electrode in an inorganic device. The method achieves black by destructive interference of external light and was disclosed in the Journal of Military and Aerospace Electronics, Volume 9, No. 6, June, 1998. But the method does not realize black to a satisfactory degree because the thickness of a thin film should be adjusted in consideration of the refractive index and absorptivity thereof.